East German Pat. No. 94,493 discloses solutions which can be converted into yarns and films. The solutions are prepared by dissolving cellulose and another polymer, such as polyacrylonitrile, in aqueous zinc chloride solutions, having a zinc chloride concentration of 30-70% and optionally containing a minor amount of an acid, such as formic acid, phosphoric acid, hydrochloric acid or the like. A disadvantage of this technique is that solutions based upon zinc chloride cause hydrolysis and therefore degradation of the cellulose polymer.
Published Japanese Patent Application No. 71/27,573, published on Aug. 10, 1971, discloses the preparation of solutions or dispersions of mixtures of cellulose and polymers such as acrylonitrile polymers in sulphur dioxide, in the presence of a tertiary or secondary amine. Because of the particular compounds used in the disclosed process, it is necessary when using such solutions to take particular precautions as regard hygiene and safety; and the solutions of this published Japanese Patent Application cannot easily be used in industrial processes.
An article by Raymond B. Seymour and Earl J. Johnson in "Struct. Solubility Relat. Polym. (Proc. Symp.), 1976, pages 241-244 (published 1977)" describes the possibility of obtaining fibres of polyacrylonitrile and cellulose from solutions. However, the starting cellulose solutions have a concentration of less than 2.5%, and it is not possible to obtain fibres having valuable textile properties from such solutions, so that the article does not lead to a process suitable for industrial production.
East German Pat. No. 89,003 teaches the preparation of stable dispersions by introducing microcrystalline cellulose into a solution of another polymer. The cellulose introduced in this manner is still in a particulate state at the fibre state, and does not contribute textile properties to the fibres.